Stein River, Mountain river in Thompson-Nicola Regional District, Canada

Stein River flows 50 kilometers from Tundra Lake through dense forests and steep cliffs before joining the Fraser River near Lytton. The system forms an unbroken river network with numerous waterfalls and narrow gorges throughout its length.

The Nlaka'pamux named the river system Stagyn, meaning hidden place, referring to the valley's concealed nature. The region has been inhabited for thousands of years and remains significant to these communities today.

The river's name comes from the Nlaka'pamux word Stagyn, meaning "hidden place", because the valley's size is not apparent from where the Stein meets the Fraser. The river and its tributaries lie within Stein Valley Nlaka'pamux Heritage Park, a name that keeps the Nlaka'pamux connection to the valley visible to visitors.

The Stein River lies entirely within Stein Valley Nlaka'pamux Heritage Park, and its lower course cuts through the mountains in a narrow gorge before reaching the Fraser north of Lytton. Access is on foot from trailheads at the valley ends; the upper river rises at remote Tundra Lake, about 1,830 m up, and passes Stein Lake.

The Stein River drains one of only two watersheds larger than 50 km² south of Prince George that have never been logged. Its valley is contained within Stein Valley Nlaka'pamux Heritage Park, and the river rises at remote Tundra Lake, about 1,830 m up, before reaching the Fraser north of Lytton.